There is no actual increase in the number of DART services at peak hours.
The existing timetable always had a few extra trains thrown in at peak, so the 0747 Bray Connolly and trains to/from Dun Laoghaire. The move to the 10 minute interval just moves these around and extends them to balance capacity out.
There is no change to level crossing downtime as the number of trains is the same between Lansdowne and Dun Laoghaire, Bray could be a bit of problem. To be fair Merrion Gates is NOT the constriction in the evening the traffic queue is mainly as a result of trying to filter onto a clogged Rock Road
Off peak is the big shift but should not be a problem, there are no public or private scheduled buses through Merrion Gates daytime (prize if you can name the only one)